The present invention relates generally to electrostatographic reproduction machines, and more particularly, concerns such a machine having a pre-fuser transport assembly for handling a wide variety of sheet weights and sizes.
In a typical toner image reproduction machine, for example an electrostatographic printing process machine, a photoconductive member is charged to a substantially uniform potential so as to sensitize the surface thereof. The charged portion of the photoconductive member is exposed to a light image of an original document being reproduced. Exposure of the charged photoconductive member selectively dissipates the charges thereon in the irradiated areas. This records an electrostatic latent image on the photoconductive member corresponding to the informational areas contained within the original document.
After the electrostatic latent image is recorded on the photoconductive member, the latent image is developed by bringing a developer material into contact therewith. Generally, the developer material comprises toner particles adhering triboelectrically to carrier granules. The toner particles are attracted from the carrier granules to the latent image forming a toner powder image on the photoconductive member. The toner powder image is then transferred from the photoconductive member to a copy sheet. The toner particles are heated to permanently affix the powder image to the copy sheet.
The foregoing generally describes a typical black and white electrostatographic printing machine. With the advent of multicolor electrophotography, it is desirable to use an architecture which comprises a plurality of image forming stations. One example of the plural image forming station architecture utilizes an image-on-image (IOI) system in which the photoreceptive member is recharged, reimaged and developed for each color separation. This charging, imaging, developing and recharging, reimaging and developing, all followed by transfer to paper, is done in a single revolution of the photoreceptor in so-called single pass machines, while multi-pass architectures form each color separation with a single charge, image and develop, with separate transfer operations for each color.
In either case, the toner image ordinarily is transferred unfused onto a copy sheet of paper, which is then picked up by a transport mechanism (a pre-fuser transport) for delivery to a fuser assembly where the toner is heated and fused to make a finished copy.
Conventional or existing pre-fuser transport mechanisms typically use rotating belts stretched between a drive shaft and an idler shaft with perforations in the belts that allow vacuum pressure from a blower to be drawn through holes in a plate below the belts, and through the belts to the sheet. The vacuum pressure assists each sheet of paper that has an image on it via electrically charged toner particles, to be pulled off the photoreceptor and acquired on the pre-fuser transport, without disturbing the unfused image on the sheet, especially in the transfer zone. The sheet is then transported and delivered to the fuser module where the toner particles are heated and pressure-fused to the sheet.
The problem with this design is that different paper weights and sizes as well as the amount of paper curl, require different amounts of air pressure for helping strip the sheet off the photoreceptor after image transfer.
Therefore, there is a need for a pre-fuser transport design that allows for varying the air pressure on the sheet responsive to sensed sheet parameters such as weight and size.
In accordance with one aspect of the present invention, there is provided a pre-fuser sheet transport assembly includes (a) an endless belt having vacuum apertures therethrough and being trained about a plurality of rollers including a drive roller; (b) a first plate located under the endless belt and including first holes formed therethrough having a first pattern, and a first size each; (c) a vacuum device for sucking air through the apertures in the endless belt and through the first pattern of the first holes in the first plate; (d) a second plate assembly including a second plate located under the first plate and including second holes having a second pattern and a second size each, the second plate being moveable laterally relative to the first plate; and (e) control apparatus for detecting and adjusting a position of the second plate relative to the first plate, and responsive to a change in a measured parameter of the copy sheet, the control apparatus including a mechanism for controllably adjusting a degree of overlap between the first holes and the second holes, thereby adjustably controlling vacuum pressure being applied to the copy sheet carrying an unfused toner image and being transported to the fuser.